The simplest solutions are often the most elegant. Designing a system to keep the Uppermost House (the 300 sq. ft. timberframe treehouse described in the award-winning book, Treehouse Chronicles), up in the air, we had two goals in mind:
- Make it simple.
- Do no harm to the tree (put no holes or fasteners in the trunk)
After tossing many ideas around, the solution we implemented met both goals beautifully. We used a combination of three simple components:
- a hexagonal steel collar
- suspended by a set of cables
- which support a series of wooden trusses
This Collar-Cable-Truss (CCT) system provides great strength and stability and is about as simple as engineering ever gets.
The structure of our tree, in part, dictated this solution. The tree is a 200 year-old white pine, nearly four feet in diameter at breast height and 105 feet tall, divides into two trunks 37 feet above the ground. At the point where the tree divides, the trunk swells to over four feet in diameter and each fork is about two feet in diameter, giving us a massive and strong anchor point for our suspension system.
So here’s how it looks:
And here’s how we put it together:
- The hexagonal steel collar (made from 1/4-inch angle iron segments) is assembled around the tree and bolted together at each corner with welded eye-bolts (safe working load over 2 tons each)
- A cable (3/8 inch) is attached to an eye-bolt (with triple cable clamps) and then run up and through the fork in the tree and down to the eye-bolt at the opposite corner of the collar. (At the fork, we ran each cable section through PVC pipe to protect the tree and spread out the load.) Three such cable segments are used, connecting all six collar corners.
- A second set of cables (5/8 inch) is connected between the centers of three of the collar segments and run up and down through the fork of the tree, just like the first cable segments. (The cummulative strength of all the collar segments gives us a safe working load of something over 15 tons.)
- Six, triangular timberframe truss segments are bolted to the center of each collar segment.
- A set of wedges is driven between the end of each truss and the trunk of the tree (this snugs the whole thing up and provides stability).
- Large horizontal wooden timbers are bolted to the vertical section of each truss and braced against the trunk (stabilizing the system and allowing us to get the trusses perfectly level).
- A wooden collar connects the lower ends of each of the trusses, mirroring the steel collar above, and tying the entire system together.
Although simple (in principle), getting all this stuff up in the tree required over six weeks of effort. In the end, we had a strong and stable 23-foot hexagon hanging in the sky and ready for its floor joists. The rest of the treehouse was easy (yeah, right).
For those of you contemplating building your own dream house in the sky, if your situation is similar to mine, you may consider using a system such as this. BUT, PLEASE BE AWARE: I am not a structural engineer and I make no claims that this system is safe. I took the advice of experts while building my treehouse. Please consult professional arborists, engineers, and builders before you try anything like this yourself.
If you have any questions, send them along. Good Luck!